Environmental fate of alkylphenols and alkylphenol ethoxylates—a review
Introduction
Alkylphenol ethoxylates (APEs) are one of the most widely used classes of surfactants. They have been used in domestic detergents, pesticide formulations and industrial products. Octylphenol ethoxylates (OPEs) and nonylphenol ethoxylates (NPEs) are two of the most common surfactants in the marketplace. APEs are discharged to wastewater treatment facilities or directly released into the environment. Primary degradation of APEs in wastewater treatment plants or in the environment generates more persistent shorter-chain APEs and alkylphenols (APs) such as nonylphenol (NP), octylphenol (OP) and AP mono- to triethoxylates (NPE1, NPE2 and NPE3) (Giger et al., 1984). Many studies have reported on the wide occurrence of APE metabolites in the environment (e.g., Ahel and Giger, 1985, Naylor et al., 1992, Bennie et al., 1997, Blackburn et al., 1999, Ferguson et al., 2001, Tabata et al., 2001).
Studies have found that APE metabolites are more toxic than the parent substances and possess the ability to mimic natural hormones by interacting with the estrogen receptor Soto et al., 1991, Jobling and Sumpter, 1993, Jobling et al., 1996, Renner, 1997. The levels of these APE metabolites present in the environment may be well above the threshold necessary to induce endocrine disruption in wildlife. These findings have raised public concern over their environmental and human health effects.
In order to assess the risks associated with these substances, it is necessary to understand the distribution and fate of APEs and their metabolites in the environment. This review will focus on current knowledge on the behaviour and fate of APE metabolites (NP, OP, NPE1–3) and related compounds in the environment.
Section snippets
Uses and exposure
APEs are a class of surfactants which are manufactured by reacting APs with ethylene oxide. An APE molecule consists of two parts: the AP and the ethoxylate (EO) moiety. This structure makes APEs soluble in water and helps disperse dirt and grease from soiled surfaces into water.
APEs can be used as detergents, wetting agents, dispersants, emulsifiers, solubilizers and foaming agents. APEs are important to a number of industrial applications, including pulp and paper, textiles, coatings,
Physicochemical properties
The physicochemical properties determine the behaviour of APE metabolites in the environment. Table 1 lists some physicochemical properties for APE metabolites (NP, NPE1–4, OP and OPE1–4). The solubility of an APE surfactant depends on the number of polar groups forming the hydrophilic part of the molecule. Lower APE oligomers (EO<5) are usually described as “water-insoluble” or lipophilic, whereas the higher oligomers are described as “water-soluble” or hydrophilic (Ahel and Giger, 1993a). The
Levels in the environment
APEs and their degradation products (e.g., NP and OP) are not produced naturally. Their presence in the environment is solely a consequence of anthropogenic activity. APs and APEs enter the environment primarily via industrial and municipal wastewater treatment plant effluents (liquid and sludge), but also due to direct discharge such as through pesticide application. The distribution of APs and their EOs has been documented in many studies in North America and Europe. NP, OP and NPEs were
Fate in the environment
APEs make up the world's third largest group of surfactants in terms of production and have been used widely in the industry for about 50 years. Concern has increased recently about the use of APEs because of the relative stability of their metabolites (NP, OP, NPE1–3) in the environment (Giger et al., 1984) and their estrogenic character to organisms like fish (Jobling and Sumpter, 1993). To assess their environmental risk, it is necessary to understand the behaviour and fate of APEs in the
Summary
(1) APEs are one of the widely used surfactants in the world. Their metabolites (NP, OP, NPE1–3) are ubiquitous in the environment because of their wide use patterns and the widespread lack of adequate wastewater treatment, and these compounds have been detected in air, water, sediment, soil and biota at differing levels in different parts of the world.
(2) Physicochemical properties indicate that APE metabolites are hydrophobic substances. They tend to bioaccumulate in lipids of organisms in
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